Android列表视图(ListView)

ListView是一个显示滚动项列表的示视图组(viewgroup)，通过使用适配器(Adapter)把这些列表项自动插入到列表中。适配器比如从一个数组或是数据库查询获取到数据，然后转换每一项成为可放入到列表的视图。

列表的显示需要三个元素：

(1) ListView：用来展示列表的view。

(2) 适配器：用来把数据映射到ListView上。

(3) 数据：具体的将被映射的字符串、图片或是基本组件。

Android列表视图(List View)

图1

对于我们如何使用适配器来动态插入view，参考链接：

http://developer.android.com/guide/topics/ui/declaring-layout.html#AdapterViews

1. 使用加载器(Using a Loader)

为了实现异步加载数据，且为了避免在查询时阻塞APP主线程，从Android3.0开始引入CursorLoader，这是一种查询Cursor的标准方式。当CursorLoader接收到Cursor结果(查询结束)，LoaderCallbacks接收到对onLoadFinished()方法的回调，此方法使用新的Cursor来更新适配器，然后列表视图显示这个结果。

虽然CursorLoader的API是从Android3.0(API 11)开始引入的，但可以通过使用支持的库来使用：http://developer.android.com/tools/extras/support-library.html，但要求Android系统版本在1.6及之后的版本。

public
class ListViewLoader
extends ListActivity

implements
LoaderManager.LoaderCallbacks<Cursor>
{

// This is the Adapter being used to display the list's data

SimpleCursorAdapter mAdapter;

// These are the Contacts rows that we will retrieve

static final
String[] PROJECTION
= new
String[] {ContactsContract.Data._ID,

ContactsContract.Data.DISPLAY_NAME};

// This is the select criteria

static final
String SELECTION =
"((" +

ContactsContract.Data.DISPLAY_NAME
+ " NOTNULL)AND ("
+

ContactsContract.Data.DISPLAY_NAME
+ " != ''))";

@Override

protected void onCreate(Bundle savedInstanceState)
{

super.onCreate(savedInstanceState);

// Create a progress bar to display whilethe list loads

ProgressBar progressBar
= new ProgressBar(this);

progressBar.setLayoutParams(new
LayoutParams(LayoutParams.WRAP_CONTENT,

LayoutParams.WRAP_CONTENT,
Gravity.CENTER));

progressBar.setIndeterminate(true);

getListView().setEmptyView(progressBar);

// Must add the progress bar to the root ofthe layout

ViewGroup root
= (ViewGroup) findViewById(android.R.id.content);

root.addView(progressBar);

// For the cursor adapter, specify whichcolumns go into which views

String[] fromColumns
= {ContactsContract.Data.DISPLAY_NAME};

int[] toViews
= {android.R.id.text1};
// The TextViewin simple_list_item_1

// Create an empty adapter we will use todisplay the loaded data.

// We pass null for the cursor, then updateit in onLoadFinished()

mAdapter =
new SimpleCursorAdapter(this,

android.R.layout.simple_list_item_1,
null,

fromColumns, toViews,
);

setListAdapter(mAdapter);

// Prepare the loader. Eitherre-connect with an existing one,

// or start a new one.

getLoaderManager,
null,
this);

}

// Called when a new Loader needs to be created

public Loader<Cursor> onCreateLoader(int
id, Bundle args)
{

// Now create and return a CursorLoaderthat will take care of

// creating a Cursor for the data beingdisplayed.

return new
CursorLoader(this,
ContactsContract.Data.CONTENT_URI,

PROJECTION, SELECTION,
null,
null);

}

// Called when a previously created loader has finished loading

public void onLoadFinished(Loader<Cursor>
loader, Cursor data)
{

// Swap the new cursor in. (Theframework will take care of closing the

// old cursor once we return.)

mAdapter.swapCursor(data);

}

// Called when a previously created loader is reset, making the dataunavailable

public void onLoaderReset(Loader<Cursor>
loader) {

// This is called when the last Cursorprovided to onLoadFinished()

// above is about to be closed. We needto make sure we are no

// longer using it.

mAdapter.swapCursor(null);

}

@Override

public void onListItemClick(ListView l,
View v,
int position,
long id) {

// Do something when a list item is clicked

}

}